The city of Brisbane braces for major damage from flooding and the massive release of water from a dam. In the town of Toowoomba, 'a wall of water' takes a heavy toll.

Reporting from Sydney, Australia — Residents of Brisbane, Australia's third-largest city, braced Wednesday for potentially monumental flooding as a river overflowed its banks from a combination of rain, runoff and the forced release of large amounts of water from a dam that had been designed to protect the city from raging storms.

At least 40,000 properties were expected to be affected by the overflowing Brisbane River, as water let out of the Wivenhoe Dam to the north bore down on the city at a rate of 7,000 cubic meters a second. A massive surge of water from the northern hinterlands overwhelmed the dam, built in the late 1970s after devastating 1974 floods, and the water was released to prevent its collapse.

"I stress the releases being made from Wivenhoe are not optional," Queensland Premier Anna Bligh said. "This is how Wivenhoe operates."

Authorities said they could not predict how high the water would rise in Brisbane but the peak, expected midafternoon Thursday, would surpass all records.

Meanwhile, in the town of Toowoomba, where a flash flood surged through the central shopping strip Monday, the official death toll rose to 14, with unofficial reports putting the number as high as 30. Ninety people remained missing in the community, less than 100 miles from Brisbane.

In Toowoomba on Monday, nearly 6 inches of rain fell in 30 minutes on already saturated land, causing the Lockyer Creek to overflow its banks.

A wave of water crashed through the town, sweeping away cars, trees, buildings and dozens of people.

"It was like a wall of water.... There was about seven or eight cars there, and just smashed them together," one man told ABC Television. "And the last I saw of it was going down the creek bobbing up and down."

With weather conditions remaining uncertain, 75% of this eastern Australian state has been declared a disaster area, and concerns continue to mount.

"Just when you think it can't get any worse, that's exactly what Mother Nature has been throwing at us over the last 48 hours," Ian Stewart, Queensland's deputy police commissioner, told ABC Television.

In Brisbane, a city of 2 million people, power was cut off to many areas and the central business district was shut down in anticipation of flooding. Panic-buying in supermarkets added to the stress.

"Right across this region, this river is creating chaos, terrifying people and causing damage already," Bligh, Queesnland's premier, said Wednesday.

Bligh had been holding news conferences every two hours throughout Tuesday evening and Wednesday, and the exhaustion showed on her face. Lightning struck the light plane in which she was traveling Tuesday as she returned from visiting affected towns.

"We are facing one of our toughest-ever tests," she said. "We will only pass this test if we are calm, if we are patient with each other … and if we listen carefully to the instructions we are being given."

In a rural area north of Brisbane, Andrew Grant, who runs camping and conference centers, said he was concerned about landslides as well as flooding.

"We've really had three days of just solid rain," he said. On the outskirts of Brisbane, water has already cut off homes and severed main roads. Sixteen-year-old high school student Zoe Miller-Starr, who lives in the suburb of Caboolture, said that on Tuesday she began the day believing she was safe. By the end of the day, she was isolated in her home, her parents stuck on a highway and her street "a swimming pool."

"Cars are floating and filling up with water and literally turning into submarines," she said. "We have no form of access whatsoever to food or medical, and that is concerning for a lot of us."

Miller-Starr's parents eventually made it home and sent her to her grandmother's house, on higher ground a few minutes away. But the only way out of the area was still by air, and she said she was concerned it might get worse.